In plastics technology, a distinction is traditionally made between three significant classes of materials, namely thermoplastics, elastomers and thermosets. In recent years, a further class of materials, the thermoplastic elastomers, has continually found new applications. Thermoplastic elastomers combine the processing properties of thermoplastics with the service properties of elastomers. The person skilled in the art is aware of various classes of these thermoplastic elastomers. A distinction can be made between two main classes, namely block copolymers (also multiblock copolymers) and elastomer alloys.
The block copolymers are composed of a hard phase and of a soft, elastic phase. The soft phases mostly form the matrix while the hard phases provide a disperse phase which acts like a crosslinking/reinforcing filler. The crosslinking regions are formed via physical bonds between the hard segments. Within their service temperatures, the block copolymers behave like crosslinked elastomers, as long as the transition temperature of the hard segments is markedly above, and that of the soft segments is markedly below, the service temperature, and the fractions in the mixture also have the correct ratio to one another.
Elastomer alloys are polymer blends which comprise thermoplastic fractions and elastomer fractions. They are produced via intensive mixing of the starting components, and crosslinking agents can be added here. If the soft phase is (to some extent) crosslinked, the term used is thermoplastic vulcanisates (TPE-V). If the soft phase has not been crosslinked, the term used if TPE-O.
The present invention relates to thermoplastic elastomers of TPE-V type. The thermoplastic used here comprises at least one copolyester as thermoplastic elastomer.
TPE-V which have copolyesters are known in the prior art.
EP 1 767 577 A1 relates to the thermoplastic elastomer compositions which have from 20 to 95% by weight of a polyester (A) with a melt flow rate of from 4 g/10 min to <20 g/10 min, and from 80 to 5% by weight of at least one rubber (B) selected from acrylate rubber (B1), hydrogenated nitrile rubber (B2) and polyether rubber (B3), where the rubber (B) has been dynamically crosslinked. The thermoplastic elastomers according to EP 1 767 577 A1 are intended, according to EP 1 767 577 A1, to feature good tensile strength properties, low compression set and superior fatigue properties. From the examples it is apparent that in particular the melt flow rate of the polyester (A) is essential for obtaining thermoplastic elastomers with advantageous properties, composed of the components according to EP 1 767 577 A1. EP 1 767 577 A1 does not disclose thermoplastic elastomers which comprise, as rubber component, specific α-olefin-vinyl acetate copolymers with vinyl acetate content ≧40% by weight
EP 0 327 010 A2 relates to thermoplastic compositions which comprise from 20 to 99 parts by weight of a thermoplastic multiblock copolyester elastomer which melts above 100° C., and from 1 to 80 parts by weight of a polyacrylate elastomer. The compositions according to EP 0 327 010 A2 are intended to be soft, elastomeric, thermoplastic materials which have a low degree of swelling in oil and a low compression set. EP0 327 010 A2 does not disclose thermoplastic elastomers which comprise α-olefin-vinyl acetate copolymers with vinyl acetate content of ≧40% by weight.
DE 44 25 944 A1 relates to thermoplastic elastomer compositions comprising (I) from 5 to 60% by weight of one or more thermoplastics selected from the group consisting of polycarbonate, polystyrene-acrylonitrile, polymethyl methacrylate, polyoxymethylene, polybutylene terephthalate, polyamide and polyvinyl chloride, and (II) from 40 to 95% by weight of a crosslinked ethylene-vinyl ester copolymer, obtainable via emulsion polymerization of ethylene and of vinyl ester monomers with polyethylenically unsaturated comonomers and, if appropriate, subsequent graft copolymerization. The advantage of the thermoplastic elastomer compositions according to DE 44 25 944 A1 is, according to the disclosure in DE 44 25 944 A1, that thermoplastic elastomers are provided which are produced via thermomechanical mixing, without any additional crosslinking step, and/or comminution step, and these have a thermomechanically stable, well defined elastomer phase structure, and good mechanical properties with improved elastic properties, at relatively high temperatures. DE 44 25 944 A1 does not mention thermoplastic elastomers in which α-olefin-vinyl acetate copolymers are dynamically crosslinked in the presence of the thermoplastic used. According to DE 44 25 944 A1, dynamic crosslinking is intended to be specifically avoided.
DE 100 17 149 A1 relates to thermoplastic elastomer compositions, encompassing (i) from 30 to 90 parts by weight of a thermoplastic resin material, which comprises at least one type of thermoplastic copolyester elastomer, and (ii) from 10 to 70 parts by weight of a rubber material, which comprises a rubber comprising an ethylene constituent. The thermoplastic polyester elastomer has a hard segment and a soft segment, and the molar ratio of a polyol moiety in the hard segment to a polyol moiety in the soft segment is 1:1.5 to less than 4.0. The thermoplastic elastomer compositions according to DE 100 17 149 A1 are intended to be suitable for joint sleeves with improved flexibility, improved compression set and improved low-temperature properties, with no impairment of the excellent mechanical properties, heat resistance and oil resistance of a thermoplastic elastomer composition. The thermoplastic elastomer compositions can comprise, as rubber comprising an ethylene constituent, an ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, ethylene-acrylate copolymer rubber, ethylene-ethyl acrylate copolymer rubber, chlorosulphonated polyethylene, chlorinated polyethylene or an ethylene-vinyl acetate copolymer rubber (EVA). The rubber material can, according to DE 100 17 149 A1, be an uncrosslinked or at least partially crosslinked material. DE 100 17 149 A1 gives an example of a thermoplastic elastomer composition which comprises, as rubber mixture, EVA and a thermoplastic copolyester elastomer, composed of dimethyl terephthalate, 1,4-butanediol and polytetramethylene glycol. The mixture comprises a proportion of 40 parts by weight of the rubber mixture and a proportion of 60 parts by weight of the thermoplastic copolyester elastomer. The rubber mixture was crosslinked using 0.5 part by weight (based on 100 parts by weight of the rubber mixture) of sulphur powder. DE 100 17 149 A1 does not disclose compositions which comprise, alongside a copolyester, α-olefin-vinyl acetate copolymers with vinyl acetate content of ≧40% by weight, where additionally at least one peroxide is present as free-radical crosslinking initiator and the proportion of the copolyester (thermoplastic polymer) is from 5 to 50% by weight.
It is an object of the present invention, in the light of the thermoplastic elastomers known in the prior art, to provide thermoplastic elastomers which feature a rubber-like property profile. This means that the intention is to provide thermoplastic elastomers, and compositions for the production of thermoplastic elastomers, where these have very good recovery properties, good tension set, good compression set, very good heat resistance values and solvent resistance values, and a low range of hardness (Shore hardness A). The thermoplastic elastomers are intended to be capable of processing via any desired processing techniques, such as extrusion, injection moulding, and also blow moulding.
None of the thermoplastic elastomers known hitherto can achieve a combination of properties comprising low hardness, good elastic properties, and rapid recovery together with solvent resistance and heat resistance. The thermoplastic elastomers known hitherto can either achieve good elastic properties or good heat resistance values, but with unsatisfactory solvent resistance values (in particular long-term solvent resistance values), or can achieve good solvent resistance values, but with unsatisfactory heat resistance values. Thermoplastic elastomers which have high heat resistance values and good solvent resistance values, such as TPE-A (polyetheramides), TPE-E (polyetheresters) and TPE-U (TPU, polyurethanes) are available only for applications in the (high) Shore D hardness range, in a high price segment, and have moderate elastic properties. None of the materials known hitherto in the thermoplastic elastomers (thermoplastic vulcanisates) class, TPE-V, has hitherto been capable of complying with the abovementioned requirements profile.